The present invention relates to a method for determining physical and/or chemical and/or biological properties of a medium and an apparatus for determining physical and/or chemical and/or biological properties of a medium.
The medium whose physical and/or chemical and/or biological properties are to be determined by a generic method is a fluid, preferably a gas, a liquid or a soft material, in particular a highly viscous, dough-like or pasty medium. The acoustic waves used to determine the properties are ultrasonic waves, for example, which are produced by an appropriate transmitter by way of a transmission signal.
In a known method for determining physical, chemical and/or biological properties of the medium, at least two acoustic waves, for example, are produced by a transmission signal, said acoustic waves propagating at least partly through the medium along identical or different propagation directions before they are each received at a receiver lying in the respective propagation direction. By way of example, in a flowing medium, acoustic waves are produced in a first propagation direction in the flow direction of the medium on the one hand and in a second propagation direction counter to the flow direction of the medium on the other hand. Then, a time-of-flight difference can be established from the reception signals generated at the respective receivers and this can be used to deduce the (mean) flow speed of the medium, for example. If, as an alternative or in addition thereto, absolute times of flight of an acoustic wave from a transmitter to a receiver are still established with the aid of the reception signals, it is possible to draw further conclusions about physical, chemical and/or biological properties of the medium, such as the density, temperature or composition thereof, for example.
WO 2008/034878 A2 has disclosed an apparatus in which acoustic surface waves are produced, said surface waves coupling volume acoustic waves into the respective medium in a waveguide. By repeatedly output coupling surface waves at the sites at which the volume acoustic wave strikes a wall surrounding the medium, acoustic surface waves are received at a receiver in turn, the times of flight and time-of-flight differences of said surface waves being characteristic for the medium and the physical, chemical and/or biological properties thereof.
Consequently, in an apparatus described in WO 2008/034878 A2 and in the method implemented therewith, the processing of the reception signals, produced at the respective receivers, for a received acoustic wave—an acoustic surface wave in this case—plays a decisive role. Thus, establishing a time-of-flight difference or an absolute time of flight from the reception signals produced at the receivers is by no means trivial and, in certain circumstances, connected to significant computational outlay. Very different methods for signal processing are used, depending on the information to be extracted from the reception signals. By way of example, the use of modulated transmission signals to be able to deduce the properties of the medium in a more reliable fashion on the basis of the obtained reception signals is known.
Otherwise, there are many (integrated or clamp-on) ultrasonic methods for measuring the flow in pipes. Clamp-on systems are attached to the pipe from the outside and therefore do not change the flow cross section. The acoustic waves always pass centrally through the pipe, which captures the entire flow profile but, as a rule, does not allow a flow profile correction. Consequently, highly accurate flow measurements are only possible in the case of known media and a simultaneous temperature and/or speed of sound measurement. Conventional multi-beam methods, such as those that emerge from DE 195 03 714 A1, EP 2 072 972 A1, EP 2 386 835 A1 or U.S. Pat. No. 4,300,401 A, for example, are able to capture the flow profile in more detail but, as a rule, do not operate without influencing the flow profile since transmitter and/or receiver are introduced into the pipe wall for the purposes of placing the sound paths.